Among the primary prostaglandins, PGD.sub.2 is a compound which shows strong biological activities like PGE.sub.2 and PGF.sub.2 .alpha.. For example, it has been found of late that PGD.sub.2 has useful activities including an antitumor activity (Japanese Patent Application Laid-open No. 124718/'83) and a somnifacient activity (R. Ueno et al., Proc. Nat. Acad. Sci., U.S.A., 80, 1735 (1983)) in addition to a platelet aggregation inhibiting activity (G. L. Bundy et al., J. Med. Chem., 26, 790 (1983)) like PGE.sub.2 and PGI.sub.2, and accordingly PGD.sub.2 is expected to introduce itself as an antitumor agent and a remedy for central nervous system disorder of a new medicinal type.
Several methods as mentioned below have hitherto been known for the production of PGD.sub.2.
(1) A method comprising the decomposition of prostaglandin endoperoxide produced by biosynthesis from arachidonic acid (see M. Hamberg et al., Proc. Nat. Acad. Sci., U.S.A., 70, 899 (1973)).
(2) A method in which PGD.sub.2 is obtained by oxidizing the 11-position of prostaglandin F.sub.2 .alpha. whose hydroxyl group at the 15-position is protected (see M. Hayashi et al., J. Org. Chem., 38, 2115 (1973)); E. E. Nishizawa et al., Prostaglandins, 9, 109 (1975)).
(3) A method in which PGD.sub.2 is obtained by oxidizing the hydroxyl group at the 11-position of prostaglandin F.sub.2 .alpha. whose hydroxyl groups at the 9- and 15-positions are protected (see D. P. Reynolais et al., Chem. Commun , 1150 (1979); R. F. Newton et al., J. Chem. Soc., Perkins I. 2055 (1981); E. F. Jenny et al., Tetrahedron Letters, 26, 2235 (1974); N. H. Andersen et al , Prostaglandins, 14, 61 (1977).
(4) A method of producing PGD.sub.2 by deprotecting the 11-actal body of PGD.sub.2 obtained from Corey lactone (see E. W. Collington et al., Tetrahedron Letters, 30, 3125 (1983)).
These methods, however, having their respective drawbacks; for instance, the method (1), in which the desired PGD.sub.2 is obtained by means of biosynthesis, may be regarded as very inefficient since this method has not only much difficulty in the handling of PG endoperoxide, the material compound, because of its lability but also much PGE.sub.2 formed as by-product in the course of the decomposition reaction. The method (2) is a method in which PGD.sub.2 is derived from PGF.sub.2 .alpha., the material compound which is a drug per se, by means of oxidation which takes place unselectively with the hydroxyl group at the 9- and 11-positions, causing the formation of a lot of by-products and the total yield from the costly material PGF.sub.2 .alpha. is only 20% at most. The method (3) is to obtain PGD.sub.2 from the material PGF.sub.2 .alpha., whose hydroxyl groups at the 9- and 15-positions are protected, derived from the intermediate formed during the making of PGF.sub.2 .alpha. through the intricate conversion of functional groups, with the faults that it requires many processes for the production and also that the total yield is low. The method (4) involves a disadvantage of making good use of only one of the produced isomers since the obtained PGD.sub.2, whose 11-position is acetalized, is mixed with the stereoisomer having a hydroxyl group at the 15-position.